Multiple drain drilling and production apparatus

ABSTRACT

Multiple drain drilling and production apparatus (16) comprising a generally cylindrical body (18) adapted to be located within a well, and an orienting assembly (24, 28) adapted to be received in the body (18) to deviate a drill string received within the body, at a predetermined depth, from a path coaxial with the body to a path at a predetermined angle to the axis of the body. The apparatus comprises at least one outlet (20) comprising a generally tubular element (42) received within the body and opening thereinto and displaceable from a first position generally coaxial with the body, into a second position at a predetermined angle thereto, by an actuator (200) received within the body, the orienting assembly being located adjacent the outlet (20).

FIELD OF THE INVENTION

The present invention relates to a multiple drain drilling andproduction apparatus and, more particularly, to such an apparatusadapted for drilling multiple drains from a single well.

BACKGROUND OF THE INVENTION

In the field of oil production it is common practice to drill a numberof branched, lateral wells or drains from a single master well. Such atechnique is used for both technical and economic reasons.

Lateral wells drilled from a single, master well enable theoil-containing strata to be reached at a number of points, so increasingboth the rate and the volume of production. Furthermore, the use of sucha technique offers economic advantages as the lateral wells all share acommon well-head and production outlet.

Another use of such drains is to make it possible to work strata havinga large number of fractures. The drains each intercept a number offractures and connect them to the drainage system of the master well.

Lateral drains are typically drilled from the master well at a pointsome distance below the surface by using a device known as a whipstock.This is a tool which serves to deviate the drillstring from the axis ofthe master well on to a new predetermined course. Having drilled a firstlateral drain, the drillstring is removed and the whipstock is turned toa new orientation and depth within the well so as to deviate thedrillstring, once it is returned within the well, on to a new course ata predetermined path relative to both the master well and the firstdrain.

The document U.S. Pat. No. 4,573,541 describes a device of this type. Inparticular, this document describes a drilling and petroleum productionstart-up device consisting of a master well and at least one branchedwell opening into the master well, and comprising an outer tube locatedin the master well, and at least one take-off assembly fastened in situin the outer tube and at least one fixed take-off tube, the lower end ofwhich communicates with a branched well. Typically, this device isadapted for drilling three branched wells from the master well.

While this device enables several branched wells to be simply drilledfrom a master well, it does present certain disadvantages. Specifically,as the three take-off tubes are arranged side by side, their diametersare necessarily small in relation to that of the master well. Similarly,should the diameter of the take-off tubes be required to be large, thereis a corresponding increase in the dimensions of the whole device.

The document EP-A-0 574 326 describes a device enabling a lateral wellto be drilled from a master well which comprises a curved surfacearranged within the device and intended to deviate a drillstring onto apredetermined path, the drillstring passing through an opening formed inthe wall of the device. However, this device does not resolve theproblem of ensuring a complete seal between the outer wall of thelateral well and that of the master well.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a multiple draindrilling apparatus which enables several drains to be simply drilledfrom a master well, while being of relatively small dimensions, andallowing the diameter of each drain to be relatively large compared tothat of the master well.

According to the invention there is provided a multiple drain drillingand production apparatus comprising a generally cylindrical body adaptedto be located within a well, orienting means adapted to be received inthe body to deviate a drill string received within the body, at apredetermined depth, from a path coaxial with the body to a path at apredetermined angle to the axis of the body, characterised in that theapparatus comprises at least one outlet means comprising a generallytubular element received within the body and opening there into anddisplaceable, from a first position generally coaxial with the body,into a second position at a predetermined angle thereto, by an actuatorreceived within the body, the orienting means being located adjacent theoutlet means.

The wall of a well is generally sealed relative to the various layers ofrock through which the well passes by a liner or casing. It is a furtherobject of the invention to provide an apparatus which ensures that theintercommunication between the interior of the well and the, or each,drain remains sealed.

According to a preferred embodiment of the invention the body is formedwith an opening for each outlet means, the apparatus further comprisesseal means arranged around the opening between each outlet means and thebody.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, withreference to the accompanying drawings in which:

FIGS. 1, 2 and 3 are schematic longitudinal views of a multiple draindrilling and production apparatus according to the invention;

FIGS. 4a and 4b are schematic longitudinal sections of the device ofFIGS. 1 to 3;

FIGS. 5a and 5b are cross sectional vie.:, taken along the lines 5a--5aand 5b--5b of FIGS. 4a and 4b respectively;

FIG. 6 is a schematic longitudinal section of an apparatus according toa second embodiment of the invention;

FIGS. 7a, 7b and 7c are schematic longitudinal sectional views of asecond embodiment of an orienting assembly;

FIG. 8 is a combined cross-sectional view, corresponding to those ofFIGS. 5a and 5b, of a second embodiment of apparatus according to theinvention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross sectional view of a well 10 which extends from thesurface (not shown). After the well has been drilled in a conventionalmanner with a constant diameter along its length, the drillstring isremoved and a reamer bit is substituted. An enlarged volume 12 is thenreamed out, beyond the original diameter, above the point from which itis desired to start the lateral drain. The drillstring and reamer bitare then removed and a casing assembly 14 is lowered into the well 10.Adjacent the lower end of the casing assembly 14, or, in the case ofmulti-zone installations, at various points along the casing assembly,is mounted a multiple drain drilling apparatus 16 according to theinvention. The apparatus comprises a generally cylindrical outer body 18whose outer diameter is the same as that of the casing assembly. Withinthe apparatus 16 are arranged one or more tubular elements or outlets 20which will be described in detail herebelow. Each outlet 20 is pivotallymounted at its upper edge on the outer body 18 and is displaceable froma first position, illustrated in FIG. 1, where it extends generallycoaxially within the body 18, into a second, open position where itprojects from the body at a predetermined angle thereto which isillustrated in FIG. 2.

When the apparatus is in the position shown in FIG. 1, a tubularactuator 22, shown in dashed lines in FIG. 1 is lowered within thecasing 14. The outer diameter of the actuator 22 is slightly smallerthan the interior diameter of the casing 14. As the actuator is loweredinside the body 18, it engages each of the outlets 20 in succession,moving them from their first position shown in FIG. 1 into their second,open position shown in FIG. 2. Each outlet may include a latching deviceto retain the outlet in its open position once the actuator iswithdrawn.

Having moved the outlets 20 into their open position, the actuator isremoved and a conventional cementing operation is carried out to fillthe annular space 21 between the casing and the wall of the well withcement. The free ends of the outlets are closed in order to avoid entryof cement from the annular space.

In order for a drill string to be caused to deviate, during a subsequentdrilling operation, down a selected one of the outlets 20, it isnecessary to locate a whipstock in the body 18 at a point adjacent theoutlet.

In FIG. 2 there is shown a orienting assembly 24 which comprises alongitudinally extending body 26, whose diameter corresponds to theinner diameter of the body 18, and whose upper end is formed with awhipstock 28 adapted to deviate a descending drill string into theadjacent outlet 20. The orienting assembly 24 may have a hollow bore toallow fluid communication therethrough. The location of the orientingassembly 24 at a given orientation and at a given level in the body 18is ensured by a conventional orientation means known as a J-slot. Insuch a device, a J-shaped recess 30, formed on the outer surface of theorienting assembly 24 engages a locating lug 32 projecting from theinner wall of the body 18 at a predetermined position. The orientingassembly 24 comprises a locating device 33, more commonly known as amuleshoe, at its lower end to guide the locating lug 32 towards thefirst J-slot. In the illustrated embodiment there are three J-shapedrecesses 30, one corresponding to each outlet.

When it is desired to drill a drain through a given outlet 20, theorienting assembly 24 is lowered into position by connventional means,for example on a drill pipe, where a preseletcted J-slot engages the lug32. For example, when it is wished to drill a drain through the lowestoutlet 20, the orienting assembly is located in the position shown inFIG. 2. Thus a descending drill string and bit will be deviated by thewhipstock 28 into the outlet 20 and drill a drain 34 along a deviatedpath shown in FIG. 3.

It should be noted that the diameter of the drain 34 is relatively largecompared to the internal diameter of the body 18, and is significantlylarger than was the case with previously proposed apparatus.

Once drilled, the drain 34 is completed and cased with a liner 36 whichis attached to the outlet 20 by a liner hanger 37 of conventionalconstruction which thus establishes sealed communication between thecased drain 34 and the body 18. The liner 36 does not project into theinterior of the body 18. Thus, the interior of the body remains clearfor subsequent operations. The orienting assembly 24 is re-positionedafter the drain has been completed and cased, in order to align thewhipstock adjacent the next outlet to be drilled through. There-positioning or actuation of the orienting assembly 24 relative to thebody 18 is accomplished by vertical displacement of the orientingassembly by conventional means such as drill pipe, coiled tubing orwireline. Such means are attached to the top of the orienting assembly24 by a releasable connecting tool (not shown). In an alternativeembodiment, the repositioning or actuation of the whipstock may becarried out by a hydraulic ram located within the orienting assembly andactuated by a control line.

After the desired number of drain wells have been drilled and completed,the orienting assembly 24 may be actuated to position the whipstock 28adjacent the drain wells previously drilled in order to removepreviously installed plugs and thereby prepare the drain wells forproduction. The orienting assembly 24 may include seals arranged aroundthe outside diameter of the body 26 in order to isolate the drain wellsone from another during the actuation of the orienting assembly. In theembodiment of FIG. 3, the orienting assembly is arranged at the lowerend of a drill string (not shown) which extends up to the surface. Whenthe orienting assembly is in its illustrated lowest position, anintermediate, tubular element is located between the orienting assemblyand the drill string so as to extend past the three outlets. The tubularelement is formed with longitudinal slots thereby allowing all the drainwells to produce into the master well.

It should be noted that in the embodiment of FIG. 3, it is possible toremove the orienting assembly 24 from the body 18. Thus, it is possibleto introduce production equipment into the master well after the drainwells have been drilled. Furthermore, it is possible, with thisembodiment, to use the orienting assembly at any time to enable a drillstring to re- enter any drain well.

FIGS. 4 and 5 show details of the construction of an outlet 20 and theway in which it is mounted in the body 18 of the multiple drain drillingand production apparatus of the invention, FIGS. 4a and 5a showing theoutlet in its closed position, and FIGS. 4b and 5b showing it in itsopen position.

In FIG. 4a there is shown, in section, the body 18 on which an outlet 20is pivotably mounted by means of a hinge 38 at a point adjacent anopening 40 in the wall of the body. The outlet 20 comprises a generallytubular part 42 mounted on a support 44 whose shape and size correspondclosely to those of the opening 40. The support is formed with anaperture corresponding to the intersection of the tubular part 42 andthe support 44 so as to allow communication between the outlet and theinterior of the body 18. A peripheral seal 46 is located in a recessformed around the edge of the support 44 and is formed of suitablematerial such as nitrile rubber or metal.

An outer casing 48 having a generally semi-circular cross section ismounted on the outer wall of the body 18 around the opening 40 and isitself formed with an opening 50 which is adapted to receive the outlet20 when it moves into its open position. A closure member 52corresponding to the shape and size of the opening 50 is attached to theouter surface of the tubular part 42. The outer casing 48 extends beyondthe periphery of the opening 40. This is more clearly shown in FIGS. 5aand 5b.

Once the apparatus is in position within the well, the actuator 22 islowered into the well until it engages the inner surface of the support.Further movement of the actuator 22 causes the outlet 20 to pivot fromits position in FIG. 4a into its open position shown in FIG. 4b. In thisopen position, seal 46 comes into contact with the inner surface of theouter casing 48, so sealing the inside of the body 18 relative to thewell. The actuator is then removed and the orienting assembly 24 islowered into the well to locate the whipstock 28 in a position, adjacentthe outlet 20, represented by dotted lines in FIG. 4b.

In some cases, such as where the apparatus is used in a deep horizontalwell, the operation of the orienting assembly may be impeded by frictionbetween it and the well. In such cases an alternative locating devicefor the whipstock is used which is illustrated in FIG. 6. This apparatushas a shorter overall length than that described above. As shown in FIG.6, the orienting assembly 24 comprises a whipstock 28 which is connectedto a separate locating element 60, or muleshoe, by a spacer 62 ofpredetermined length. The locating element 60 is adapted to seat itselfon the locating lug 32 when the assembly is lowered into the well by anyconventional means. The length of the spacer determines the distancebetween the whipstock 28 and the locating lug 32, and thus by selectingthe length of the spacer 62 the whipstock can be located adjacent achosen outlet. The descending drillbit will be deviated by the whipstockand drill a drain along a predetermined path. Subsequent drains can bedrilled by selecting spacers of appropriate lengths and which locate thewhipstock with an orientation corresponding precisely to that of theselected outlet.

In the embodiment described with reference to FIGS. 4 and 5, the outlet20 is pivotally mounted within the body 18, and the resulting assemblyforms part of the casing string being lowered into the well. Analternative embodiment to the above comprises an outlet which isconstructed separately from the body. After the casing has been loweredinto the well and located in position, the outlet would be run insidethe casing with an adapted running tool, until it reaches a positionadjacent a desired, pre-machined opening. Such an opening would becompletely closed by a closure member. The sealed junction between theouter casing and the closure member would be made of a fissile materialsuch as an epoxy resin. A special opening tool would then be used tolaterally translate the outlet through the pre-machined opening, thusbreaking the fissile material and pushing the closure member outwardsrelative to the outer casing.

In the embodiment of FIG. 2, the body 26 was located and aligned in thebody 18 by means of a conventional orienting means known as a J-slot.FIGS. 7A, 7B and 7C show elements of a second embodiment of orientingassembly which presents the advantage of leaving the casing bore free ofany internal restriction over its whole length, as the locating lug isno longer required. The body 18 is formed, at a predetermined pointbelow the desired opening 40, with a location region 70 comprising anumber of recesses 72 set in the inner wall of the body 18. Theparticular disposition of the recesses 72 is associated with a givenlocation region 70. At a predetermined point in the body below thelocation region 70 is formed a muleshoe 74. FIG. 7B shows a locatingassembly 76 adapted to be received and located in the location region70. The locating assembly 76 comprises a plurality of identical keys 78,arranged about a sleeve 79 which is slideably mounted on the outersurface of a central, cylindrical body 80, the keys being urged radiallyoutwards into their illustrated position by springs 82. In use, thelocating assembly 76 is lowered down, within the body 18 until itreacher the position illustrated in FIG. 7C in which the keys 78 engagethe corresponding recesses 72 formed on the i surface of the body 18..It should be noted that, since the keys 78 will only engage recesses 72having the corresponding shape, the locating assembly can be lowereddown the well, past location regions adapted to receive other locatingassemblies, without the keys engaging the recesses and blocking thelocating assembly in position. Thus, a given locating assembly will onlyseat itself in a predetermined, given location region in the body.

Once the locating assembly 76 has been seated in the predeterminedlocation region, further downward motion will cause the cylindrical body80 to slide axially relative to the sleeve 79, against the force ofspring 84, into a position where the lower end 86 of the cylindricalbody extends beyond the end of the sleeve 79. In this position, alocating lug 88, which is normally held closed and protected by thesleeve against the force of springs 90, is free to extend radiallyoutwardly from the lower end 86 beyond the sleeve 79. From thisposition, further downward movement of the cylindrical body 80 willcause the locating lug 88 to engage a downwardly extending slot 92 inthe mule shoe 74. Thus, the locating assembly 76 can be positioned at apredetermined point, and with a predetermined orientation, in the body18. Having correctly positioned the locating assembly 76, it is a simplematter to locate the outlet 20 and the whipstock 28 at a desiredposition in the body, above the locating assembly. In order to preventany possible movement of the assembly 76 and the whipstock 28 once theyhave been positioned inside the body, it is envisaged to fit the mandrelof the locating assembly 76 with a releasable anchoring device whichwould be located between the whipstock 28 and the locating assembly 76.Such an anchoring assembly would comprise a compressible rubber elementwhich would prevent formation cuttings from being deposited in therecesses 72 set in the inner wall of the body 18.

In FIG. 8, there is shown a second embodiment of an apparatus accordingto the invention which ensures that, when the outlet 20 is in its openposition, the interior of the body 18 remains completely sealed withrespect to the well, and, furthermore, ensures that the structuralintegrity of the body remains satisfactory.

In FIG. 8 it will be noted that the edge 96 of the opening 40 is formedwith an internal recess 98 extending, in the wall of region 94, in thedirection of opening of the outlet 20, as shown by arrow 95. A support100, whose shape and size correspond to those of the opening 40, isformed with projecting lugs 102 which extend along its edges. When theoutlet 20 is opened, and the support 100 moves to fill the opening 40,the projecting lugs 102 mate with the corresponding recesses 98. Thisinterengagement between the support 100 and the wall of body 18 servesto strengthen the apparatus and make it more resistant to bursting.Furthermore, the edge 96 of the opening 40 extends at a slight angle,preferably 5°, to the direction of opening shown by arrow 95. The edgeof support 100 is formed at a corresponding angle. This choice of angleassists in centering the support 100 in the opening 40. Instead ofarranging the seal 46 along the outer surface of the support 100, as wasthe case in the embodiment of FIGS. 5a and 5b, the seal 46 extends alongthe edges 104 of the support 100. This has the advantage of protectingthe seal from mechanical damage when the outlet is in its closedposition. In addition, a spring mounted latch 106 is mounted along eachside of the opening 40 in the wall of region 94 to ensure that theoutlet 20 remains in its open position shown in FIG. 8b. A set oflatches 106a could alternatively be mounted on the outer edge of thesupport 100.

In the embodiments of FIGS. 1 to 5, the outlets 20 were moved from theirclosed position to their open position by a tubular actuator 22 lowereddown within the body from the surface. This actuator had an externaldiameter closely similar to the internal diameter of the body in orderto ensure the complete displacement of the outlet into its openposition. This necessarily close fit of the actuator in the body couldresult in the actuator becoming jammed during its descent into position.In order to overcome this problem, an alternative type of actuator canbe used in which an inflatable packer of conventional design is arrangedat the lower end of the drillstring having a considerably lesserdiameter than that of the tubular actuator 22. Once the packer has beenlowered into position, adjacent the outlet 20 to be opened, fluidpressure is applied to the interior of the packer, from the surface, byway of the drillstring. This pressure causes the packer to inflate,whereby its diameter considerably increases, pushing on the support44;100 and opening the outlet. The packer can then be deflated, allowingit to be brought back up to the surface.

In the case where horizontal, or steeply inclined wells, traverse alayer of reservoir rock, it is desirable to drill several drains, eachof which extend generally horizontally within the layer in order toproduce a maximum quantity of oil from the reservoir. With thepreviously described embodiments of the invention, it is not alwayspossible to align the outlet into the desired direction simply byorienting the casing into a predetermined angular position at thesurface. This problem arises due to friction between the casing and thewall of the well. Thus, it is desirable to provide a way to allow theapparatus and, in particular, a given outlet, to be located in apredetermined angular position.

According to a further aspect of the invention, the body 18, containingat least one outlet 20, may form a separate sub-assembly. Thissub-assembly is mounted on the lower end of the casing 14 by means of aswivel joint i.e. a joint which allows the sub-assembly to rotate, aboutits longitudinal axis, relative to the casing. The sub-assembly isfitted with an internal locating device, for example that shown in theembodiment of FIG. 7, which allows a locating member, arranged at theend of a drillstring lowered down within the casing, to fixedly engagethe sub-assembly. Thus, once the end of the drillstring has interengagedthe sub-assembly, rotation of the upper end of the drillstring at thesurface will cause the sub-assembly to rotate relative to the casing andto its surroundings. Using conventional measurement-while-drillingtechniques, which incorporate inertial and magnetic measuring devices,it is possible to determine the precise angular position of thesub-assembly and thus correctly move it into its desired, predeterminedposition by controlled rotation of the drillstring. A device known as areversing tool, which is used for mechanical backing-off applications,may advantageously be incorporated between the drillstring and thesub-assembly. This device includes a planetary gearing system which, forexample, transforms two rotations of the drillstring into one rotationof the sub-assembly. Such a system allows greater precision in theangular orientation of an outlet by rotation of the drillstring.

According to a still further aspect of the invention, an alternate meansof causing the sub-assembly to rotate relative to the casing may beprovided. This embodiment requires the reaming out of an enlarged volume12 along a greater axial length than in previous embodiments. In thisembodiment, the external surface of the sub-assembly is formed with oneor more outwardly projecting helical blades or rails which extend, inthe manner of an Archimedes screw, longitudinally along thesub-assembly. When the sub-assembly has been lowered into position, theedge of the blades come into contact with the wall of the well. Furtheraxial displacement of the casing and the sub-assembly in eitherdirection will be accompanied by a corresponding rotation of thesub-assembly which is brought about by the interengagement of thehelical blades and the wall of the well. The precise angular position ofthe sub-assembly can be determined using conventional means aspreviously described.

When the assembly is lowered into the well there is a risk that thefluid pressure within the casing might inadvertently open the outlet.Thus, the outlet could advantageously be fitted with a locking meanssuch as a shear pin 108 to hold it in its closed position. The actuatorfor the outlet would therefore further comprise means to release thelocking means once the actuator is in its lowered position. Furthermoreit is envisaged that the outlet 20 and its closure member 52 be formedfrom a single piece. This would further strengthen the assembly and makeit more resistant to collapse. A seal 107 could also be incorporatedbetween the closure member 52 and the edge 96 of the opening 40.

In order to give greater flexibility to the apparatus in accordance withthe invention, it may advantageously be constructed from individualunits, each containing a single outlet. Each individual unit would beconnected to an adjacent unit by a sub-assembly. Thus, a composite body18 could be assembled, for example on the drilling site, so as tocomprise a desired number of outlets having a given axial separation andangular orientation.

It is envisaged that the apparatus of the present invention may be usedwith existing wells, that is wells already fitted with a conventionalcasing. In such a case the existing well's casing is section milled atthe desired depth and undereamed to the appropriate diameter over theappropriate length. The body 18 of the apparatus is mounted on a shortsection of casing, having a diameter less than the internal diameter ofthe existing casing, which is hung into the existing well at theappropriate depth. An orienting assembly having a whipstock mounted on acylindrical spacer is then lowered into the well by conventional means.The use of the apparatus in existing wells gives the advantage that itallows increased production in wells that might otherwise be decliningin production.

It is further envisaged that the present apparatus be used with drillstrings of reduced diameter, that is less than 12 cm, the dimensions ofthe apparatus being reduced accordingly.

We claim:
 1. Multiple drain drilling and production apparatus (16)comprising a generally cylindrical casing (18) adapted to be locatedwithin a well, orienting means (24,28) adapted to be received in thecasing (18) to deviate a drill string received within the casing, at apredetermined depth, from a path coaxial with the casing to a path at apredetermined angle to the axis of the casing, characterised in that theapparatus comprises at least one outlet means (20) comprising agenerally tubular element (42) located within the casing and forming apart thereof and opening thereinto, and the generally tubular elementbeing operatively associated with the casing to be displaceable from afirst position generally coaxial with the casing, into a second positionat a predetermined angle thereto, by an actuator (22) received withinthe casing, and the orienting means (24,28) being located adjacent theoutlet means (20).
 2. Apparatus according to claim 1 characterised inthat the casing (18) is formed with an opening (40) for each outletmeans, the apparatus further comprising seal means (46) arranged aroundthe opening between each outlet means (20) and the casing (18). 3.Apparatus according to claim 2 characterised in that the casing (18)comprises an outer casing (48) mounted around the opening (40), eachoutlet means (20) being formed with a support (44) adapted to close theopening (40) when the outlet means is in its second position, the sealmeans (46) being located on the support (44).
 4. Apparatus according toany one of claims 1 to 3 characterised in that the orienting means (24)comprises a whipstock (28), and a body (26,60) which is adapted toengage a locating lug (32) arranged within the casing (18) so as tolocate the whipstock at a predetermined position within the casing (18).5. Apparatus according to claim 1 further comprising three outlet means(20), each arranged with a predetermined orientation relative to thecasing (18).
 6. Apparatus according to claim 1 characterized in that theactuator (22) comprises a tube (22) received within the casing (18). 7.Apparatus according to claim 1 characterized in that the actuator (22)comprises an inflatable packer received within the casing (18). 8.Apparatus according to claim 3 characterised in that the casingcomprises a closure member (52) for the opening (40) when the tubularelement (42) is in its first position.
 9. Apparatus according to claim 8further comprising a seal between the outer casing (48) and the closuremember (52).
 10. Apparatus according to claim 1, further comprising:anopening preformed in the casing; and the outlet means is operative to bedisplaceable through the opening.
 11. Apparatus according to claim 1characterized in that the generally tubular element (42) is retained inits second position by a spring mounted latch (106).
 12. Apparatusaccording to claim 1 characterized in that the apparatus comprises asub-assembly, adapted to be rotatably mounted on an end of a casinglocated within the well.
 13. Multiple drain drilling and productionapparatus (16) comprising a generally cylindrical casing (18) adapted tobe located within a well, orienting means (24,28) adapted to be receivedin the casing (18) to deviate a drill string received within the casing,at a predetermined depth, from a path coaxial with the casing to a pathat a predetermined angle to the axis of the casing and forming a partthereof and characterised in that the apparatus comprises at least oneoutlet means (20) comprising a generally tubular element (42) locatedwithin the casing and opening thereinto, and displaceable from a firstposition generally coaxial with the casing, into a second position at apredetermined angle thereto, by an actuator (22) received within thecasing, the orienting means (24,28) being located adjacent the outletmeans (20);the casing (18) being formed with an opening (40) for eachoutlet means, the apparatus further comprising seal means (46) arrangedaround the opening between each outlet means (20) and the casing (18);the casing (18) further comprising an outer casing (48) mounted aroundthe opening (40), each outlet means (20) being formed with a support(44) adapted to close the opening (40) when the outlet means is in itssecond position, the seal means (46) being located on the support (44);the casing (18) further comprising a closure member (52) for the opening(40) when the tubular element (42) is in its first position; and a sealmade from fissile material between the outer casing (48) and the closuremember (52).